Both FOB not working, car would not start

I have a 2000 Freelander 1.8Lt petrol engine. Last year I started to have problem with both FOB's unable to lock or unlock the car and when the key inserted and turned the dashboard comes alive and the horn works as well as the windscreen wipers, lights all work but turning the key the engine would not start.
I then removed the battery and let it charge but still same problem. I left and returned to the car 6 months later, I reconnected the battery and all was working fine for 3 days, but I never locked the car with the FOB's but than accidentally I push the lock button on a FOB the door was open and I heard the usual click in rapid sequence for the door lock and the all story started again, no lock or unlock, engine will not start etc.
I have replaced the batteries on both the FOB's I also coupled the battery with another car battery (jump wires) to give an extra boost, but nothing worked.
I am thinking of 1) the immobiliser, 2) the ECU, 3) radio receiver for FOB's
Before buying any of these I would like to hear if anybody has had a similar experience or has any suggestion.
Thank you
Maurizio

You will need someone to plug a reader??

check for water in the ecu?? (All your main electrical systems??

Kev

Badger688 said:

You will need someone to plug a reader??

check for water in the ecu?? (All your main electrical systems??

Kev

Click to expand...

Thank you for your reply, would a car that old have a plug where to connect this reader? I have checked all the fuses and fuse box, I do not see any moisture around the engine nor around the ECu but I will double check , be thing I did not do is to check that the ground is firmly connected to the chassis I just ensured that both plus and minus were tight on the battery not the other end. How does this reader look like ? If I may ask ?
Thank you again for your time

Kev, by the way I forgot I have a Veepeak OBDcheck BLE+ and in fact I saw on a youtube post the location of the ODB port, I will give it a try, I saw someone posted the list of error codes so with that I will be able to do a bit of a diagnostic